1. Field of the Invention
The present invention relates to diagnostics and controls for voltage bias applications in electrophotographic imaging systems, and more particularly to those systems employing feedback of load bias to regulate voltage.
2. Description Relative to the Prior Art
In an electrophotographic imaging systems, the movement of toner is controlled in part through electrostatic forces. Components of the system are biased at different electrical potentials in order to set up fields to attract or repel electrostatically charged toner particles. The loss of bias, or incorrect bias, on parts of the system can adversely impact the quality of the image produced by the system.
One source of faults in the biased systems is arcing between surfaces at different potentials. This disturbs the bias potential. Some high voltage systems detect arcing and indicate errors. Other systems monitor the output of the bias power supply to check for disturbances in the voltage. While these prior art systems are basically effective for their intended purposes, they ignore one of the prime sources of failure that occurs within rotating biased components. Failure occurs in contact used within rotating biased components. This failure can be caused by wear of the brushes used to apply bias to the rotating component. In systems where rotating biased components are removed on a regular basis, electrical connectors wear and have an especially strong chance of potential failure. Systems having multiple imaging units employed to produce multiple color images can be very difficult to troubleshoot and determine where a fault is occurring. The simple evaluation of defects after they have occurred is not a workable solution. There needs to be a diagnostic tool available to evaluate bias problems before they result in defects. Once the defect has occurred, it is simply too late.
An example of a prior art teaching for controlling voltages within image forming apparatus is U.S. Pat. No. 5,132,869, issued to Nakaya (Nakaya). This reference illustrates one prior art method for controlling voltages that are applied to components within electrophotographic apparatus by keeping current at a predetermined level. Nakaya accomplishes this control by using timing configurations to the control pulse width modulation in response to the detected output voltage. However, the actual component to which power is applied to is not closely observed. Instead, the voltage across the component is observed. Nakaya discloses a manner for the current regulation of corona charging loads charges that are regulated within Nakaya by monitoring the actual drum current to ground through a sensing element placed between the drum and ground. The current to that sensing element is then monitored periodically by machine control, and the constant voltage output of the corona charger power source is adjusted. Nakaya senses the current returning to the power supply from the machine ground (or the grid bias output of the primary charger). The output voltage is continuously adjusted to regulate the current that the charger delivers. (Column 6, line 15 of Nakaya describes this as part of the current control.) This is a common technique used within the prior art for current regulated corona charger power supplies. While Nakaya is effective to adjust output voltages within certain limits, this prior art teaching does little to indicate problems within components using rotating contacts.
In view of the foregoing description, it should be apparent that there remains a need within the prior art for a system that can assist in identifying potential problems within rotating biased components. It is, therefore, desirable to employ diagnostics on these systems having rotating biased components to provide status feedback to the machine""s control unit when any type of bias fault has occurred. The system could then respond to this fault signal making it possible to stop imaging and alert the machine operator that bias faults may adversely affect the image quality of the prints being produced.
The invention provides a method and apparatus for detecting biasing faults within components for electrophotographic equipment including: open load, over load, shorted load and intermittent contact with the load or arcing conditions, as well as power supply output failure in a bias system.
A digital signal is provided to a machine control system indicative of a biasing condition within a component. The machine control system can sense the signal by either interrupt or polling (periodic sampling) methods. The sensed signal can be appropriately filtered with software. The result is that all of these bias failures may be detected automatically by machine control, thus preventing the machine from producing additional prints with degraded image quality. The system also provides a method to alert the operator service personnel on which area of the machine to service. This is particularly useful for enabling the operator to replace cartridges in the machine that need replenishment. In a machine with multiple imaging modules, with each of the modules having multiple loads that are biased, a fault analysis system is necessary to enable efficient servicing of the machine. The present invention addresses the problems within the prior art by providing an indication that a problem has occurred in order that action may be taken to prevent image quality defects.
The invention employs a feedback of the load bias potential to the source of the potential for voltage-regulated biases. This feedback may be repeated for a multiplicity of loads and sources throughout a system. The feedback from the load is compared with the expected output of the bias source. If the difference between the expected bias and the bias feedback from the load is beyond a predetermined range, the bias source will send a signal to the machine controller that indicates a bias fault has occurred. The invention allows for the bias potential to be adjusted automatically within the machine and for the fault detection limits to adjust to the new set point.
The present invention monitors the output voltage of the current regulated outputs via a sample of a scaled analog representation of the signal. When the voltage falls above or below a range defined in software, the machine control detects this as an error. The machine is shutdown when this occurs, and the operator/service person is informed of which system has indicated an error state.